Guiding a flexible web, e.g., paper, thin plastic sheets, metal foil, etc., through a device, e.g., a printer, such that the web stays in registration with a functional component of the device that is to act on the web, e.g., a printer head or web cutter, is difficult. The drive force that advances the web downstream, e.g., a grit textured drive roller with spring-loaded rubber nip roller, can also produce a side force. The magnitude of this side force is a function of a number of variables including roller alignment, irregular nip pressure, and the friction between the drive/nip rollers and the web.
The long-standing response to this problem of a side force acting on a web advancing through a device so as to move the web in a sideways manner and thus lose registration of the web within the device is the use of one or more edge guides. U.S. Pat. No. 3,968,917 teaches the use of an edge guide comprising a base plate secured to an edge plate in an L-shaped configuration such that one lateral edge of a relatively stiff web is always in contact with the edge plate as it passes over the base plate. U.S. Pat. No. 4,069,959 teaches a web guide apparatus that includes a steering frame over which a traveling web is passed and which is pivotally mounted to a stationary support frame. U.S. Pat. No. 4,534,523 teaches tape guides which comprise cylinders with shoulders on each end. The tape passes over the cylinders and between the shoulders as it advances through a tape cartridge. U.S. Pat. No. 4,795,070 teaches a mechanism for maintaining a moving web in its proper path along an edge guide. The edge guide is a simple flattened U-shaped plate pivotally supported on a frame and that can pivot about an axis perpendicular to the moving web. U.S. Pat. No. 5,055,874 teaches a film flattening apparatus that comprises, among other things, edge guides opposite one another and mounted on a base. The guides are simple plates extending above the base and in contact with the lateral edges of the advancing film.
U.S. Pat. No. 5,279,454 teaches a system of establishing the lateral position of a web without requiring the web path to change direction. The system comprises a lateral edge guide joined to a support surface to form an obtuse angle. The angle is obtuse to prevent escape of the advancing web, and the support surface is curved in its transverse direction concave towards the web. A roller is positioned against the support surface so as to urge the advancing web against the lateral edge guide.
Still other edge guides are known in the art. U.S. Pat. No. 5,657,983 teaches a registration guide member with a wear-resistant inboard surface. U.S. Pat. No. 5,701,171 teaches a pair of oppositely facing, substantially parallel edge guides supported by a frame, each edge guide comprising a serpentine contact surface with a central portion for engaging an edge surface of a web moving between the guides. U.S. Pat. No. 5,938,190 teaches a replaceable media guide for use with a sheet feeding mechanism. The media guide includes a support plate, an edge guide projecting substantially at right angles from the support plate, and a first sheet engaging a friction pad engaged with the support plate. U.S. Pat. No. 6,068,418 teaches a retractable outer edge guide for use with a print station and a guide path extending from the station to a media roll station. U.S. Pat. No. 6,501,620 teaches an edge guide with top and bottom guide surfaces for engaging the top and bottom edges of a web as it passes through the guide. The edge guide is used in combination with a face guide.
Standard edge guides for printers have one of two profiles, i.e., flat and concave. Edge guides with a flat profile are basically plates fastened perpendicular to the web-supporting platform. Edge guides with a concave profile have a square cavity as shown in FIG. 1. Edge guide 10 comprises interior surfaces 12a, 12b and 12c which define rectangular cavity 11. Flexible web 13 moves over a support platform (not shown) and due to side force 14, moves over lower surface 12a and into cavity 11. Flexible web 13 continues to move over lower surface 12a until it encounters vertical surface 12b at which point it bends and moves over vertical surface 12b until it encounters top surface 12c. Upon encountering top surface 12c, web 13 bends again and forms web curl 15 which is frequently the source of a web jam or web tear.
The standard edge guide is a simple and desirable tool for maintaining a flexible web in registration with another component of a device as the web advances through the device, but a better design is of interest to the extent that it results in reduced or elimination of web jams or web tears.